In recent years, lithium-ion batteries, nickel-hydrogen batteries and other secondary batteries have become increasingly important as vehicle-mounted power sources or power sources for personal computers and portable devices. Lithium-ion batteries are particularly promising as high-output vehicle-mounted power sources because they provide high energy densities with low weight. In a lithium-ion battery, charge and discharge are accomplished by means of the back-and-forth movement of lithium ions between positive and negative electrodes.
In a typical configuration, this kind of lithium-ion secondary battery has an electrode body (wound electrode body) comprising sheet electrodes wound in a spiral. In this wound electrode body, as shown in FIG. 11 for example, negative electrode sheet 1 having a structure in which negative active material layers 3a and 3b each containing a negative active material are supported on both sides of negative electrode collector 2, and positive electrode sheet 4 having a structure in which positive active material layers 6a and 6b each containing a positive active material are supported on both sides of positive electrode collector 5, are wound in a spiral with separators 8a and 8b therebetween. Patent Documents 1 to 4 are examples of prior art relating to batteries provided with this kind of wound electrode body.